Symptoms of overdose and/or acute systemic toxicity involves central nervous system toxicity that presents with symptoms of increasing severity ^L5930. Patients may present initially with circumoral paraesthesia, numbness of the tongue, light-headedness, hyperacusis, and tinnitus ^L5930. Visual disturbance and muscular tremors or muscle twitching are more serious and precede the onset of generalized convulsions ^L5930. These signs must not be mistaken for neurotic behavior ^L5930. Unconsciousness and grand mal convulsions may follow, which may last from a few seconds to several minutes ^L5930. Hypoxia and hypercapnia occur rapidly following convulsions due to increased muscular activity, together with the interference with normal respiration and loss of the airway ^L5930. In severe cases, apnoea may occur. Acidosis increases the toxic effects of local anesthetics ^L5930. Effects on the cardiovascular system may be seen in severe cases ^L5930. Hypotension, bradycardia, arrhythmia and cardiac arrest may occur as a result of high systemic concentrations, with potentially fatal outcome ^L5930.

Pregnancy Category B has been established for the use of lidocaine in pregnancy, although there are no formal, adequate, and well-controlled studies in pregnant women ^F4349. General consideration should be given to this fact before administering lidocaine to women of childbearing potential, especially during early pregnancy when maximum organogenesis takes place ^F4349. Ultimately, although animal studies have revealed no evidence of harm to the fetus, lidocaine should not be administered during early pregnancy unless the benefits are considered to outweigh the risks ^L5930. Lidocaine readily crosses the placental barrier after epidural or intravenous administration to the mother ^L5930. The ratio of umbilical to maternal venous concentration is 0.5 to 0.6 ^L5930. The fetus appears to be capable of metabolizing lidocaine at term ^L5930. The elimination half-life in the newborn of the drug received in utero is about three hours, compared with 100 minutes in the adult ^L5930. Elevated lidocaine levels may persist in the newborn for at least 48 hours after delivery ^L5930. Fetal bradycardia or tachycardia, neonatal bradycardia, hypotonia or respiratory depression may occur ^L5930.

Local anesthetics rapidly cross the placenta and when used for epidural, paracervical, pudendal or caudal block anesthesia, can cause varying degrees of maternal, fetal and neonatal toxicity ^F4349. The potential for toxicity depends upon the procedure performed, the type and amount of drug used, and the technique of drug administration ^F4349. Adverse reactions in the parturient, fetus and neonate involve alterations of the central nervous system, peripheral vascular tone, and cardiac function ^F4349.

Maternal hypotension has resulted from regional anesthesia ^F4349. Local anesthetics produce vasodilation by blocking sympathetic nerves ^F4349. Elevating the patient’s legs and positioning her on her left side will help prevent decreases in blood pressure ^F4349. The fetal heart rate also should be monitored continuously, and electronic fetal monitoring is highly advisable ^F4349.

Epidural, spinal, paracervical, or pudendal anesthesia may alter the forces of parturition through changes in uterine contractility or maternal expulsive efforts ^F4349. In one study, paracervical block anesthesia was associated with a decrease in the mean duration of first stage labor and facilitation of cervical dilation ^F4349. However, spinal and epidural anesthesia have also been reported to prolong the second stage of labor by removing the parturient’s reflex urge to bear down or by interfering with motor function ^F4349. The use of obstetrical anesthesia may increase the need for forceps assistance ^F4349.

The use of some local anesthetic drug products during labor and delivery may be followed by diminished muscle strength and tone for the first day or two of life ^F4349. The long-term significance of these observations is unknown ^F4349. Fetal bradycardia may occur in 20 to 30 percent of patients receiving paracervical nerve block anesthesia with the amide-type local anesthetics and may be associated with fetal acidosis ^F4349. Fetal heart rate should always be monitored during paracervical anesthesia ^F4349. The physician should weigh the possible advantages against risks when considering a paracervical block in prematurity, toxemia of pregnancy, and fetal distress ^F4349. Careful adherence to the recommended dosage is of the utmost importance in obstetrical paracervical block ^F4349. Failure to achieve adequate analgesia with recommended doses should arouse suspicion of intravascular or fetal intracranial injection ^F4349. Cases compatible with unintended fetal intracranial injection of local anesthetic solution have been reported following intended paracervical or pudendal block or both. Babies so affected present with unexplained neonatal depression at birth, which correlates with high local anesthetic serum levels, and often manifest seizures within six hours ^F4349. Prompt use of supportive measures combined with forced urinary excretion of the local anesthetic has been used successfully to manage this complication ^F4349.

It is not known whether this drug is excreted in human milk ^F4349. Because many drugs are excreted in human milk, caution should be exercised when lidocaine is administered to a nursing woman ^F4349.

Dosages in children should be reduced, commensurate with age, body weight and physical condition ^F4349.

The oral LD 50 of lidocaine HCl in non-fasted female rats is 459 (346-773) mg/kg (as the salt) and 214 (159-324) mg/kg (as the salt) in fasted female rats ^F4349.